Jewelry Guide

How to Choose a Perfect Blue Diamond for Your Engagement Ring

Blue diamond engagement ring

Some of the most famous diamonds in history, like the Hope Diamond, are blue diamonds. Blue diamonds are prestigious and luxurious, and beyond the reach of most of our budgets. This is because these stones are among the most expensive of all colored diamond varieties.

If you’re lucky enough to afford one, a blue diamond makes for a classy, elegant and distinct engagement ring that’ll stand out on your finger. Synthetic or treated blue diamonds are excellent alternatives to get the look without breaking the bank.

In this comprehensive buying guide to blue diamonds, we will take a detailed look at all the major factors you need to be aware of before you make the purchase of a lifetime.

  1. Why are Blue Diamonds Blue?

Of all the fancy colored diamonds, blue diamonds are spectacular and as we said before, among the rarest of the colored diamonds. Diamonds are the result of pressurized and heated carbon atoms. But what gives a diamond its blue hue?

The answer is the rare element boron (which makes up only about 0.001% of the earth’s crust). The diamond will obtain a bluish color if the nitrogen content is low and there is boron present during its formation. If there is a higher concentration of boron, the intensity of the blue color will be higher as well, making the stone even more valuable.

Some blue diamonds appear green or gray. Greenish blue diamonds can get their color from radiation and nitrogen impurities while hydrogen present during the stone’s formation can cause the stone to acquire a grayish tone. Naturally occurring pure blue diamonds are extremely rare to find. Most blue diamonds on the market have secondary hues in addition to the primary bluish hue.

  1. Why are Blue Diamonds a Good Choice for Engagement Rings?

Blue diamond close up

A rare blue diamond on James Allen. See it here.

On a practical note, blue diamonds are extremely durable and scratch-resistant, and are perfect for daily wear. Also, the fire and sparkle of a blue diamond is unmatched by other blue gemstones making them ideal for a center stone.

From a symbolic standpoint, blue diamonds represent faithfulness, sincerity and loyalty – ideal characteristics for a relationship about to take a new direction. This makes them ideal for engagement rings.

Another thing to consider is the value and prestige of a blue diamond engagement ring. This would stand out, different to all other engagement rings you know making it highly desirable.

Although it is very expensive to buy a natural blue diamond engagement ring, treated and lab-grown blue diamonds are excellent less expensive alternatives with hardly any distinguishable difference with a natural blue diamond (more on this later).

  1. Grading the Color of a Blue Diamond

Marquise shape grayish-blue diamond close up

Blue diamond with grayish tints. See it here.

Of the 4Cs used to grade diamonds, cut is king for colorless diamonds. But for colored diamonds, color is the most important C.

It can be difficult to evaluate the color of a blue diamond, as often there are more than one colors present. In order to identify the exact color grade, the three main aspects to take note of are hue, tone and saturation.


This refers to the primary color, or visible tint of the stone. In the case of blue diamonds, blue would be the hue of the stone. As we mentioned before, there can be other hues present as well. Gray and green are the most common secondary hues present in blue diamonds. If these tones overpower the blue, the overall value of the stone can be affected. Pure colored diamonds are unique and very expensive.


This refers to how light or dark the stone is. If the stone is too light, it will appear faint and the color will not be vivid. If, on the other hand, the stone is too dark, it may come across as being more black than blue. Choosing the tone comes down to personal preference, but the best stones have a tone that is neither too dark nor too light.

Blue diamond intensity chart

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This refers to how strong the color of the stone is. It goes without saying that the deeper and more vivid the blue color is, the higher the price of the stone.

Once these three aspects have been evaluated and graded, a specific color grade on the color scale for fancy-colored diamonds can be assigned to the stone.

The color grade scale is as follows: Faint, Very Light, Light, Fancy Light, Fancy, Fancy Intense, Fancy Vivid, Fancy Dark, and Fancy Deep

This image shows blue diamonds with a range of color combinations.

  1. Blue Diamond Vs. Blue Sapphire – Is There a difference?

Blue sapphire and diamond engagement ring in white gold

Blue sapphire is the most popular blue gemstone for engagement rings. See this ring here.

Although many people compare blue diamonds to sapphires and believe they are in many ways the same, these two types of stones are very different. Here are the main differences:

  • Blue diamonds rank 10 on the Moh’s scale while sapphires have a hardness ranking of 9. Although the difference in hardness is only by one grade, there are implications of this. Firstly, sapphires may need cleaning or polishing more often than a blue diamond. Second, blue diamonds are more durable than sapphires and are more scratch-resistant. 
  • Blue diamonds are much rarer than sapphires. They’re extremely rare and valuable. To put this in perspective, at the time of this writing, we couldn’t find a handful of blue diamonds across all the online retailers that offer these stones. 
  • Blue diamonds are more brilliant and have greater sparkle than sapphires due to their superior ability to refract light. Although sapphires have a very good sparkle, they are not as bright as blue diamonds, and when dirty, their sparkle can be easily dulled. 
  • They differ in terms of their chemical composition. Blue diamonds are made of carbon with traces of boron, nitrogen or hydrogen whereas sapphires are formed from corundum (aluminum oxide).

Whether you choose a sapphire or a blue diamond is totally dependent on your personal preference and most importantly budget. While both stones are excellent choices for engagement rings, blue diamonds are definitely more brilliant and have that extra sparkle.

  1. Should I Buy a Treated Blue Diamond?

Because natural blue diamonds are very hard to find, it can be difficult to find one to suit your specifications and budget. Treated blue diamonds are an excellent alternative to natural blue diamonds.

It is important to note that these enhanced diamonds are not fake. In fact, many blue diamonds on the market are treated colorless diamonds. These are enhanced using irradiation, heat and pressure to produce the blue color in the stone. Often the stones treated in this way have a very saturated appearance. It is totally fine to buy an enhanced blue diamond, as long as you know its origin.

When buying a treated stone, ensure that you request for the grading report, from a reputable lab such as GIA or IGS. This certificate will verify whether or not the stone is natural and if it has been treated. As you would guess, treated diamonds are cheaper than natural blue diamonds, so make sure you know the origin of the stone you are buying to avoid overpaying.

  1. What is Synthetic (lab-created) Blue Diamond?

An excellent alternative to natural blue diamonds is synthetic blue diamonds. These are stones that have the exact same chemical composition as a naturally occurring diamond with the only distinguishing feature being that they were created in a lab.

These stones come with many benefits. For one thing, they can be 20% to 50% less expensive than natural blue diamonds. As if this isn’t good enough, synthetic diamonds also have a much lower direct impact on the environment, making them an eco-friendly choice. They are also conflict-free and you can be assured that the diamond is ethically sourced. Granted they may not have the same romance that a natural diamond, formed over many thousands of years, may have. But as a practical and beautiful choice, synthetic diamonds are second to none.

Lab diamonds are graded in the same way as mined diamonds. Look for a report from an independent grading lab such as GIA or IGI. They will contain information of the 4Cs as well as details of its origin. If you are looking for a large stone, a treated blue diamond may give you more options to choose from, as it can be difficult to find synthetic blue diamonds over 2 carats. Also the price can grow exponentially high for large stones.

  1. Cut Grading of Blue Diamond

For blue diamonds the cut’s importance is in relation to its color. The cut of a blue diamond can impact the appearance of the color, which is why blue diamonds (or any fancy colored stone for that matter) are cut in such a way as to bring out the best color of the stone. This means that cut proportions considered ideal for colorless diamonds may be different for blue diamonds. In short, the focus when cutting a blue diamond is not on the brilliance but on the color.

  1. Evaluating the Clarity of Your Blue Diamond

As with cut, clarity for a blue diamond is also not as important as it is for a white diamond. The reason is that blue diamonds are able to hide flaws to some degree due to their color. When purchasing a blue diamond, you may be able to drop down a few grades on the clarity scale and still have an eye-clean stone. You can evaluate the clarity by checking whether or not the stone has visible flaws.

Finally, always exercise caution when shopping for a blue diamond. As they are so rare and valuable, ensure that you are buying from a reputed vendor and that you have been provided with a grading report from a third party such as GIA. Whether you choose a natural, synthetic or enhanced blue diamond, make sure you know the origin of the stone.

Where to Find Blue Diamonds

Finding a blue diamond is hard because of how rare they are. However, sites like James Allen and Blue Nile often have a small collection of blue diamonds on offer. At the time of this writing, James Allen has 8 blue diamonds on offer and Blue Nile has 10.

Jewelry Guide